Alan Sipress -- If swine flu joins bird flu, the flu pandemic may be much worse

When swine flu erupted this spring in the southwestern United States and Mexico, it had been 40 years since the last flu pandemic. The outbreak has dispelled any illusion that pandemic influenza belonged to a bygone era, like smallpox, polio or scarlet fever. But we haven't seen how bad things might yet get.

What's the worst-case scenario? It could be a continuing vaccine shortage. It might be a mutation in the swine flu virus that suddenly makes the strain resistant to Tamiflu, as some seasonal flu strains already are. Or it could be that hospital ICUs become so overwhelmed that people who could have been saved die.

These are all unnerving possibilities. Yet many flu specialists say their real nightmare is that swine flu could meet up and swap genetic material -- or reassort, as these scientists say -- with another, deadlier flu strain, breeding a new virus that is as contagious as H1N1 but far more savage.

Such a strain is already circulating in Asia and Africa, and it could be ready for a chance encounter with swine flu. It is called bird flu. Unlike swine flu, which is no worse than a seasonal flu bug for most people, bird flu kills more than half of those who contract it: While there have been only 460 confirmed human cases of bird flu, 268 of those people died. And even more than swine flu, bird flu preys on the young and healthy, ravaging their lungs, a modus operandi reminiscent of the 1918 flu that killed as many as 50 million people.

So far, scientists haven't found proof that swine and bird flu are about to merge and spawn a deadlier virus. But the prospect is so chilling that health officials have been warning about it since earlier this year. Margaret Chan, director general of the World Health Organization, urged public health experts not to take their eyes off H5N1 bird flu even as H1N1 swine flu was sweeping the globe this spring. "No one can say how this avian virus will behave when pressured by large numbers of people infected with the new H1N1 virus," she told an assembly of the world's top health officials in May. Separately, she appealed to Asian health ministers: "Do not drop the ball on monitoring H5N1."

Influenza is a cruel wonder of nature, one of the most promiscuous microbes. Its viruses have a rare gift for swapping genetic material with each other. This is because the genetic material in a flu virus -- unlike in nearly all other viruses -- is composed of segments that can be individually replaced. If two different strains invade the same cell, they can trade attributes, then dispatch that progeny back into the world. And so the WHO and other health agencies are watching closely as swine flu spreads to countries where bird flu is well established, in particular Egypt and Vietnam.

As a correspondent, I tracked the bird flu virus for several years starting in early 2004. My travels took me across nine Asian countries, from jungle villages to squalid urban quarters, through run-down hospitals and cutting-edge labs. Along the way, I discovered how economic, political and cultural realities were conspiring to imperil us. In a single generation, East Asia's surging demand for protein has led to an explosion in poultry farming, and these flocks have become perfect breeding grounds for a pandemic strain. At the same time, age-old customs have facilitated the virus's spread.

In Thailand, I went to cockfights at makeshift arenas to see how fans crowd around birds that may be carrying the disease. I visited breeders of fighting cocks, witnessing how they cradle the birds, wiping down their bloodied feathers and even sucking mucus from their beaks. At live poultry markets in Indonesia, China and Vietnam, where the air was rank with the odor of chickens and ducks, and the floors slick with their blood, I saw how people and livestock were crammed together, a crucial nexus in the spread of the virus.

Despite the threat to humanity, several Asian countries (notably China, Indonesia, Thailand and Vietnam) covered up their bird flu outbreaks, in some instances until it was too late to contain the virus's spread. Subsequently, these governments claimed to have cornered the virus. But it keeps coming back -- fresh reports are circulating about renewed outbreaks among poultry in Indonesia and Thailand -- and each time it does, it gets another chance to reassort with another virus.

And now, along comes swine flu. Although its mortality rate is well below 1 percent, there have already been tens of millions of cases worldwide. Is this more-contagious virus the key that might unlock bird flu's terrible full potential? The swine flu virus is so new that researchers have yet to plumb its secrets. How exactly does it pass from one person to another? How does it attack the human body, and why, in a small percentage of cases, is this assault catastrophic? Could it reassort with another flu strain?

This summer, scientists from the University of Maryland, the Virginia-Maryland Regional College of Veterinary Medicine and the National University of Colombia published the results of their swine flu research on ferrets. (Ferrets are widely used in flu research because they are susceptible to human flu viruses and display some of the same symptoms as people.) The study suggested that swine flu is unlikely to reassort with ordinary seasonal strains and instead is more apt to crowd them out. We can only hope that it will be equally chaste when it comes to bird flu.

But another study, also published this summer, offers reason to worry about bird flu's potential for a sinister tryst with another virus. The research showed that bird flu has the ability to reassort with at least some other strains of flu. A team at the Centers for Disease Control and Prevention in Atlanta confirmed this by simultaneously infecting ferrets with bird flu and a strain of ordinary seasonal flu. When they later tested secretions from the ferrets' noses, the researchers found that they carried new flu strains that contained genetic material from both of the parent strains.

We cannot confidently predict the twists and turns of the flu virus, which has repeatedly confounded some of the world's brightest scientists. No one expected that bird flu would leap from birds to humans -- until it did. Its initial, withering attack on a young boy in Hong Kong 12 years ago was like a "visitation from outer space," according to flu specialist Keiji Fukuda, who was dispatched by the CDC to investigate the initial occurrences.

He recalled how the Hong Kong outbreak eluded understanding, even as it spread and began resembling the 1918 Spanish flu. "You feel like: 'I don't know what is going to happen. I don't know what is going on. But what is going on is not good, and it reminds me of the worst not-good of the century,' " he said. Today, Fukuda is WHO's top flu official and says he remains humbled by flu's stubborn unpredictability.

Already, the swine flu epidemic has chastened us by revealing the sorry state of our antiquated technology for producing vaccines and the limits of our brittle, underfunded system for emergency medical care. But swine flu is not merely a warning shot. The virus itself could be the catalyst for a new flu -- and an even deadlier pandemic.

Alan Sipress is the economics editor of The Washington Post and the author of "The Fatal Strain: On the Trail of Avian Flu and the Coming Pandemic."